The present invention relates to a power drive system for driving a sliding door in movement between an open and a closed position. It is particularly directed to a position encoder for a drive arrangement which accommodates shifting between manual and positively driven powered operation of the door at any position along its path of movement. While useful in other applications, the power drive system of the present invention is especially well adapted for use in operating the sliding door of a van type vehicle.
All power drive systems for sliding doors require a power system capable of driving an output member coupled to the door in either direction over a relatively long working stroke. In addition to the foregoing consideration applicable to sliding doors in general, further problems are presented where the drive is to power the sliding door of a van.
In the van application of the power drive system, the sliding door is conventionally mounted at the passenger side of the van and a major convenience of the system is that it may be power operated by control switches accessible from the driver's seat. However, if the driver is outside the van loading or unloading articles through the sliding door, the power controls are out of reach and there are many occasions where, in this situation, the driver will want to open or close the door manually. If the door is positively mechanically linked to the power source of the drive, this connection will interfere with manual operation of the door and, in the case of certain types of control systems, disturb a relationship between the door and drive relied upon by the control system to energize the drive motor when the door is at certain positions on its path of travel.
Since the door may be left in the fully closed or fully open positions or any position therebetween through either manual or powered movement, it is important that the actual position of the door be known at all times. This is necessary so that subsequent activation of the power controls will cause the door to move in the desired direction to a fully opened or fully closed position regardless of the door's starting position. Previously devised power door controls have utilized electromechanical limit switches to detect the fully closed and/or fully opened positions of the doors. However, no information was provided regarding the position of the door between either of these two positions.
Automatic power drive systems for other movable vehicle panels, such as vehicle windows, are also known. One such power window drive is manufactured by Kostal GmbH & Co., KG., Federal Republic of Germany. In this drive unit, an encoder has a shaft fixedly coupled to the window drive motor output shaft. The shaft rotates upon rotation of the drive motor output shaft and causes rotation of a circular member of the encoder. An open slot is formed in the circular member of the encoder which extends approximately one half around the circumference of the circular member. Two pairs of spaced, side-by-side mounted photoelectric emitters and receivers are mounted in the encoder on opposite sides of the slot and the adjacent solid portion of the circular member. Rotation of the circular member upon rotation of the window drive motor causes the light beams between each emitter and receiver pair to be alternately broken as the slot and solid portions of the circular member rotate between each emitter and receiver pair. Signals from the photoelectric pairs indicative of the number of times the light beams are broken are input to a processor which counts the number of such signals to deactivate the window drive motor when the window reaches the full opened or full closed positions. The direction of movement of the window is determined by the processor through the detection of the sequence of signals from the emitter and receiver photoelectric pairs.
This control unit can also be programmed to detect a stopped or impeded movement of the window while the direction selection switches are still depressed so as to automatically deactivate the drive motor, such as when an obstruction is met by the window moving to the fully closed position.
The position encoder of the present invention presents a practical solution to the problems discussed above.